The present method is directed to making bonding bumps, for example, gold bumps on electrical substrates such as semiconductor chips where the chips are to be bonded to an interconnect board using tape-automated-bonding or flip chip technology.
Recently, most of the high performance electronic systems demand that either tape-automated-bonding (TAB) or flip chip bonding (FCB) be used as compared to wire bonding to attach the chip leads to the high density interconnect boards. These types of bonding require that the chip interconnect pads be higher than the rest of the chip so as to have thicker metal bumps (anywhere between 1 and 20 microns thicker than 1 micron thick aluminum required for wire bonding). However, chips normally have only thin metal pads for wire bonding and are not available with thick bumps. Thick bumps can be manufactured by the time-consuming process of photolithography using either a bump plating process of lift-off process.
The present invention provides a method of fabrication of bumps by using a direct metal writing tool by depositing bumps with a focused liquid metal cluster ion beam source.